Hey guys, new smoker here. I've used the smoker twice (actually on my second time as I type this) and each time the smoker rolls well for about a half hour and then the amount of smoke coming out goes to almost nothing. The thermometer that it came with (I know, I'll replace it soon) says between 250 and 300. I've tried with the chip tray uncovered and covered with the piece it comes with. Any ideas what I am doing wrong?